A/N: Hi guys! Random Doctor Who and Sonic crossover, cuz I have this theory that if the Doctor was there he'd have saved Cosmo.
And a big thanks to my friend Rhiannon, who helped me with the plot
Crying Children
The last of his kind, and a thousand years old (at least), the Doctor and his blue box were at Amy Pond's house. The TARDIS was out in the garden and the Doctor was on the sofa with River, who cringed as he ate fish fingers and custard. Amy grimaced as the Doctor offered her a fish finger but accepted it, dipping it in the custard and eating it.
"The worst part is… it's actually quite tasty…" she said, through a mouthful of food. The others laughed.
Rory knocked on the front door, having gone out shopping and forgotten his keys. "You're hopeless," Amy giggled, opening the door and kissing her husband.
Rory frowned. "Have you been eating fish custard?"
"Hello, daddy," the Doctor teased.
"Oh, God," Rory groaned.
"Oh come on Rory, you know you missed me," the exclaimed loudly, hugging his father-in-law.
"Right," Rory said, dumping his shopping on the kitchen table. "Sure. But, ah… what's he doing here?" he asked, finally able to duck out of the hug.
"Yeah," Amy added in a suspicious tone of voice. "Why did you drop in on us, Doctor?"
The Doctor put on an offended face. "Can't I just randomly drop by to visit my amazing mother-in-law, gorgeous wife, and you, without some sort of ulterior motive?"
"Not unless there's some ultra-secret medicine that only affects time Lords in the custard," River commented lazily, stretching out on the sofa and covering the Doctor's spot with her legs.
The three of them stared him down until he finally gave up. "Dyah, okay," he exclaimed. "I was going through the time vortex and there was this interference from another universe and I thought you might like to check it out with me because you're so awesome and… I don't want to go on my own," he whined, giving his friends the puppy-dog eyes.
Amy and River gave him the exact same amused smirk, knowing that the Doctor simply couldn't resist anything as interesting as interference from another universe, while Rory stared in open-mouthed surprise, still trying to figure out what the Doctor was on about. To someone who wasn't used to people who spoke at a hundred miles an hour about stuff that belonged in a science fiction story, talking to the Doctor had the possibility of causing a major brain meltdown.
"Please?" the Doctor begged, in his whiniest voice.
"Oh, alright," Amy said at last.
"I'll go too," River sang, hugging the Doctor from behind.
"I don't think that's such a good –"
"Oh c'mon Rory," Amy pouted. "You're not scared to go on a little adventure, are you?"
"It's not adventure I'm scared of," Rory replied patiently. "It's the lot of us being killed by some dalek-man… thing that I–"
"There's no such thing as a dalek-man," the Doctor corrected. "Actually, it's a very disturbing idea…"
"C'mon daddy," River said in her most persuasive voice. "How long has it been since we went on an adventure?"
Rory paused for a minute, trying to think of a counter-argument. Finally, he said: "But every time we go on adventures something bad happens. The first time, I ended up dead… then Amy and River got kidnapped, then –"
"Okay, okay, you've made your point," the Doctor said, walking around Rory. "But here's the thing: I'm not giving you a choice."
And the Doctor proceeded to push Rory towards the garden and into the TARDIS. Rory tried to grab onto doorframes and get help from his wife and his daughter, but the Doctor was stronger and the girls simply followed, laughing.
"Alright," the Doctor said when he, Rory, Amy and River were finally in the TARDIS. "Let's get this show on the road!"
Soon they were flying through the time vortex. River was helping (much to the Doctor's amusement) and Amy and Rory stood there awkwardly, watching the monitors.
"Damn it!" the Doctor yelled, almost kicking the console in frustration. "I can't find it! Where was it?"
River rolled her eyes and started to fly the TARDIS herself, pushing the Doctor out of the way until a strange kind of blip appeared on one of the monitors. "Is this it, sweetie?"
"Yeah," the Doctor said, half glad to have found it and half frustrated that he couldn't do it himself. "A tears between this universe and another one. Looks interesting."
"Are we going through?" Amy asked.
"Of course," River and the Doctor said simultaneously, grinning at her.
"Hold on tight," the Doctor said, already working the console again.
"You'll have to if he's flying," River teased, correcting the Doctor's mistakes.
For a horrible few minutes the TARDIS shook violently, as if something was attempting to pull it apart, but finally it stopped and they were sailing smooth, near a planet. The Doctor focused a monitor. The planet was full of very short, friendly-looking aliens selling talismans and future-seeing things.
"I recognise this place," Amy said. "Remember, Rory? From that show when we were twelve? Sonic X?"
"Sonic X?" Rory scoffed. "Is that even possible?"
The monitor caught a blue blur running around the planet at the speed of sound. "Looks like it," River commented.
"So what's going on in this universe that we need to get involved with?" the Doctor asked, frowning.
"I think I know," Amy said. "It's the Metarex. Those PO'd robots the plant guys turn into, remember, Rory?"
"Eh? I think so… but how would that tear open a universe?"
"Because they stole all the planet eggs."
"But that doesn't make any –"
"Look Rory," Amy said, "it's spacey-wacey, alright? It doesn't have to make sense. Right, Doctor?"
"Couldn't have said it better myself," the Doctor said. His voice sounded distant, like he was thinking of something else. He was staring at another monitor.
"Everything alright, sweetie?" asked River; but the Doctor left quickly. She turned the monitor round to face her and smiled slightly. "Of course."
An eight-year-old Seedarian girl was centred on the monitor, running away from her friend – a yellow, two-tailed kitsune who the people aboard the TARDIS instantly recognised as Tails.
"Isn't that Cosmo? The girl from Season three, who Tails had a crush on?" River asked.
"Yeah," Amy said, smiling fondly. "She's crying."
The Doctor stopped the girl as she ran and knelt down to her height. "Are you alright?" he asked with a friendly smile. "Don't worry, it's okay; I can help. I'm the Doctor."
"I'm not alright, and you can't help," the girl sobbed. "I've just found out I'm going to cause all my friends pain and there is no way to stop it."
"Oh, I'm sure there's a way," the Doctor said. "There's always a way. What's going to happen?"
"Spoilers," teased a voice from behind the Doctor, who turned around and greeted River with a "Hello sweetie."
"Don't worry," River promised Cosmo. "You'll be fine. We'll see you soon." And she dragged the Doctor away.
"Cosmo!" Tails panted, catching up to her once more. "Are you okay?"
"I'm not sure…" Cosmo said vacantly, watching as the two strange people vanished into a blue box which, in turn, vanished.
"Who was that?"
"A very strange man," Cosmo answered. "But he seemed very kind. I'm sorry I ran off, Tails."
"Okay, let me see if I've got this right," the Doctor said, leaning against the TARDIS' console and rubbing his temples. "This is the universe of a cartoon and that girl I just talked to is the last of her kind, and is supposed to die to save everyone."
"Yeah," Amy shrugged from her perch on the metal rail.
"Oh no," the Doctor fretted. "That means we're interfering where we shouldn't be… we should get out of here, right now!"
"Not so fast, Doctor!" Amy exclaimed. "River promised to help, and I didn't raise her as a girl who goes back on her promises!"
The Doctor didn't point out the irony of the word choice: that River had been taken away so early, Amy had barely been able to raise her in the first place.
"Why don't you show him what'll happen if we don't, Sexy?" River said to the TARDIS, using the name the blue box had given to herself when she'd been in a human body.
The TARDIS had clearly heard River, because the image on one of the monitors flickered and changed to a shot from the last episode: one where Tails shot Cosmo and cried.
"This episode always made me cry," Amy said. "I always used to think The Raggedy Doctor could have saved her, you know."
The others watched the time Lord's face. They could see his resolve disappearing. The Doctor couldn't just stand there while children cried.
"When is this?" the Doctor asked at last. His voice was very quiet; and breaking slightly.
Cosmo was in her tree form and was listening to her friends trying to persuade Tails to shoot her when another voice appeared in her head: the voice of the strange man with the blue box. "It's okay; I'm going to save you," the man's voice said. "You need Tails to shoot and I'll pull you out at the last second. You'll revert to your previous child form. Okay?"
Cosmo nodded. Somehow she trusted this man – the Doctor. "Okay."
Trying to persuade Tails to shoot was painful. Not physically, but it made her heart sad, because he would really believe he was shooting her. Cosmo really did care about Tails. She didn't want him to be sad.
And then – and then he agreed. He fired and something happened, like she had turned into light, just as the laser was about to hit.
And suddenly Cosmo found herself laying on a metal-grate floor. Around her were four people: the strange man; the curly-haired blonde woman; a young red-haired woman and a young man.
The Doctor helped her up. "Sorry for not telling you the plan sooner. It kind of… was developed in the space of about five seconds. Let's get you back to a planet, eh? Where to, Amy?"
"Mobius," the red-haired woman answered. "Probably a couple of months from now, when everyone's back there."
"Wait!" Cosmo said. "I won't see my friends for months?"
"Well, no," the Doctor answered. "They won't see you for months. You won't see them for a couple of minutes."
"That doesn't make any sense."
"Time machine," the blonde woman answered quickly, rushing over to a complicated-looking console. The red-haired woman – Amy, was she called? – knelt in front of Cosmo. "You gonna be okay?"
"Yes. But could I talk to Tails first? I must tell him that I'm alright."
"Okay, but I can only give you a couple of minutes."
Tails heard a strange noise outside his workshop but ignored it. He didn't honestly care. He missed Cosmo too much – he still couldn't believe he'd shot her. He felt terrible for doing it. How could he?
"What's wrong?" a voice asked. Tails looked up – it was that strange man he had seen Cosmo talking to once. "D'you miss someone?" the man asked. Tails nodded.
"Cosmo," he choked out. "I – I shot her! I didn't want to but she asked me to…"
He dissolved into tears and the man hugged him. "I'm sure you did the right thing," the man said.
"But I loved her," Tails sobbed. "And I never even got to tell –"
"Hey, don't worry," the man said. "You can trust me, I promise. I'm the Doctor."
"But –"
"It's okay. You can still tell her."
"No I –"
"Look." The Doctor stopped hugging Tails and stood aside. Tails glanced up briefly, blinked several times and looked again.
Surely not. It couldn't be… surely it wasn't… "Cosmo?"
"Tails!" the Seedarian exclaimed, flinging herself at him and hugging him so suddenly he almost stopped breathing from surprise.
"But… how… how are you here?" Tails asked, stunned.
"The Doctor saved me," Cosmo grinned. Tails turned back to the strange man.
"Thank you," he muttered, surprised. "But I still don't understand… why?"
"I'm old," the Doctor answered. "I'm a very old man, and the last of my kind. I just want to help. I'll be going now, but I got here by fluke. I won't be coming back."
Cosmo and Tails hugged the Doctor gratefully and the Time Lord smiled softly as he walked back to the TARDIS with his friends.
When the Doctor's blue box was gone, Cosmo looked carefully at Tails and saw that he had been crying for a long time. She knew she had been away for at least two months, although to her it had been five, maybe ten minutes.
"Oh…" Cosmo cradled Tails and gently rocked him, letting him cry if he needed to. Tails held her back and buried his face in her shoulder.
"I missed you, Cosmo," Tails sobbed.
"Ssh. Don't be sad."
"I love you," Tails muttered.
Cosmo smiled and kissed Tails' forehead. "I love you, too."